1. Field of the Invention
This invention relates to the field of switching voltage regulators, and particularly to multi-phase switching voltage regulators.
2. Description of the Related Art
Switching voltage regulators provide a predetermined and substantially constant output voltage from a source voltage that may be fluctuating, or that may be at an inappropriate amplitude for the load. Such regulators typically employ one or more switching elements. The switching elements may be, for example, field-effect transistor (FET) switches. Control circuitry regulates the current supplied to the load by varying the ON-OFF times of the switching elements (i.e., the regulator's duty cycle, which is the percentage of time that a switch is ON during a cycle of operation). Inductors and capacitors are typically used to convert the switched current pulses into a steady flow of load current. Switching regulators are frequently used in portable battery-powered electronic products, as they provide high operating efficiency and long battery life with little heat generation.
A switching voltage regulator may be arranged to operate using one or more different relegation modes. For example, for voltage-mode regulation, a feedback signal Vfb which varies with the regulator's output voltage is fed to a comparator along with a periodic sawtooth waveform; the comparator's output controls the duty cycle of the switching elements. For current-mode regulation, a voltage Vi is generated which is proportional to the current in the output inductor. Vi and Vfb are provided as inputs to a comparator, the output of which controls the duty cycle of the switching elements.
Several methods have been employed to obtain inductor current information for use in a switching regulator's control loop. Typically, a small voltage is sensed, either continuously or periodically sampled, to determine the current. One approach is described in U.S. Pat. No. 5,982,160 to Walters et al., in which an R-C network is connected across the output indicator, with the small resulting signal sent to the controller. Another approach is described in U.S. Pat. No. 5,847554 to Wilcox et al., which samples the voltage drop across the regulator's MOSFET switches when they are on.
Advanced microprocessors require power supplies that provide a low voltage (e.g., <2 volts) at high current. One way in which high currents are provided is with a multi-phase switching regulator, in which the components of a number (N) of single-phase regulators are repeated to produce N output currents, which are summed together to provide the total output current. However, implementing any of the regulators cited above as a multi-phase regulator requires summing and/or sampling data in the controller IC, which can introduce unwanted complexity and processing delays into the IC design.
Another switching regulator issue concerns maintaining the output voltage within specified limits in response to load transients. One approach to this problem is known as “adaptive voltage positioning” (AVP), in which the output voltage is positioned within the specified range so that it best withstands a load transient. This is conventionally accomplished by establishing a “droop impedance” for the output, by inserting information about the desired output current droop into the output voltage feedback loop as an error signal. However, this approach can result in sluggish and imprecise control on the output voltage for dynamic changes in the load.